Binutils Documentation

Introduction to Binutils

Binutils, short for Binary Utilities, is a set of programming tools for manipulating binary files. These tools are essential for software development, particularly in compiled languages, as they handle tasks such as assembling, linking, and analyzing executable code and object files. This documentation provides an in-depth guide to the various components of the binutils suite, their functionalities, and practical usage examples.

The binutils package is a fundamental component of many development environments, especially those that rely on the GNU toolchain. Understanding binutils is crucial for low-level programming, debugging, and performance optimization.

Key Components of Binutils

The binutils suite consists of several powerful tools, each designed for a specific purpose:

1. Assembler (as)

The GNU assembler (as) translates assembly language source code into object files. It supports a wide range of processor architectures and assembly syntaxes.

  • Functionality: Converts human-readable assembly code into machine code.
  • Usage: as my_program.s -o my_program.o

2. Linker (ld)

The GNU linker (ld) combines one or more object files and libraries to create a single executable file or another object file. It resolves symbol references between different object files.

  • Functionality: Merges object files, resolves external references, and produces executables.
  • Usage: ld my_program.o -o my_program

3. Binary File Inspector (objdump)

objdump displays information from object files. It can disassemble code, display symbol tables, show section headers, and more.

  • Functionality: Provides detailed analysis of binary files.
  • Common Commands:
    • Disassemble code: objdump -d my_program.o
    • Show symbol table: objdump -t my_program.o
    • Show section headers: objdump -h my_program.o

4. Symbol Table Utility (nm)

nm lists the symbols from object files. Symbols can be functions, variables, or other defined entities.

  • Functionality: Lists symbols and their types.
  • Usage: nm my_program.o

5. Readelf

readelf displays information about ELF (Executable and Linkable Format) files. ELF is a common standard for object files, executables, and shared libraries on Unix-like systems.

  • Functionality: Detailed inspection of ELF files.
  • Usage: readelf -a my_program

6. Size

size prints the size of sections in bytes for each object file.

  • Functionality: Reports the size of code, data, and other sections.
  • Usage: size my_program.o

7. Strings

strings prints the printable character sequences from binary files. This is useful for finding embedded text strings within executables or object files.

  • Functionality: Extracts human-readable strings.
  • Usage: strings my_program

Common Use Cases and Examples

Debugging Corrupt Binaries

When encountering issues with executables or object files, tools like objdump and nm can help identify problems with symbol tables, sections, or code. 


# Check for undefined symbols after linking
ld my_obj1.o my_obj2.o -o my_program

# If linking fails, use nm to inspect symbols
nm my_obj1.o
nm my_obj2.o

Analyzing Executable Structure

Understand the composition of your compiled programs. 


# View all information about an ELF executable
readelf -a my_executable

# Disassemble the code section to see assembly instructions
objdump -d my_executable

Extracting Information

Find embedded strings or analyze the memory layout. 


# Find all printable strings in an executable
strings my_program

# Get the size of different sections
size my_program.o
Tip: For complex linking scenarios, consult the ld manual page for advanced options like script files and library searching paths.

Advanced Topics

  • Linker Scripts: Customizing the linking process.
  • Relocation: How addresses are adjusted during linking.
  • Debugging Symbols: Using DWARF or stabs formats for debugging.
  • Cross-Compilation: Building binaries for different architectures.

Refer to the official GNU Binutils documentation for comprehensive details on these advanced subjects.

Note: Binutils are primarily command-line tools. Their integration with IDEs (like Visual Studio or VS Code) typically happens through build systems and compiler toolchains.